Mycobacterium tuberculosis, the primary etiologic agent of tuberculosis, causes one of the most important diseases in the world from the standpoint of human morbidity and mortality. In the past decade, it has emerged as a major opportunistic infection in patients with AIDS. Multidrug-resistant M. tuberculosis poses a major threat to the public health. The development of new preventative or therapeutic strategies to combat this pathogen requires more knowledge about M. tuberculosis molecules that play a key role in bacterial physiology and pathogenesis. Such molecules include exochelins, low molecular weight iron-binding peptides of M. tuberculosis, about which little is known. In preliminary investigations with our collaborators on this project (Marcus Horwitz and Joseph Reeve, UCLA), we have succeeded in purifying the major exochelins from M. tuberculosis so as to allow their structural, biological and immunochemical characterization. The specific aim of this particular sub-contract research project is to determine the composition and structure of the major exochelins of M. tuberculosis using advanced mass spectrometry.